President Bush said yesterday that he would consider using the military to "effect a quarantine" in the event of an outbreak of pandemic influenza in the United States.

Responding to a question during a news conference, Bush also suggested that putting National Guard troops under federal, rather than state, control might be one part of a response to the "catastrophe" of an avian influenza outbreak.

The president raised the same idea after Hurricane Katrina, suggesting that he is considering a greater role for the military in natural disasters.

The president gave no details on the specific role troops might play or what sort of quarantine might be invoked. The federal government's pandemic-response plan, the product of more than a year of work, is expected to be released soon.

Most public health experts believe it is impossible to entirely isolate neighborhoods, towns, cities or regions during an outbreak of disease. Instead, quarantines today generally refer to a variety of strategies for identifying and limiting the movement of people who are infected with a contagious pathogen or are at high risk.

That might include screening travelers for fever and flu symptoms; prohibiting large gatherings of people, including at some workplaces; and requiring that people exposed to infected individuals stay at home until the incubation period for the illness has passed. China took these measures during the outbreak of severe acute respiratory syndrome in 2003.

"The policy questions for a president in dealing with an avian flu outbreak are difficult," Bush said. "One example:

If we had an outbreak somewhere in the United States, do we not then quarantine that part of the country? And how do you, then, enforce a quarantine? . . . And who best to be able to effect a quarantine?"

He did not answer his own questions, but after the last one, he said: "One option is the use of a military that's able to plan and move. So that's why I put it on the table. I think it's an important debate for Congress to have."

The president said some governors object to the idea of federal control of state National Guard units in emergencies.

He added that, as a former governor, "I understand that. . . . But Congress needs to take a look at circumstances that may need to vest the capacity of the president to move beyond that debate. And one such catastrophe or one such challenge could be an avian flu outbreak."

A strain of avian influenza called H5N1 has led to the death of more than 140 million birds in Asia. It has infected 116 people, of whom 60 have died.

The government is stockpiling antiviral medications and an experimental "bird flu" vaccine as a defense against the virus, should it develop the capacity to spread easily and quickly in human beings.